Electro-absorption modulators (EAM) are commonly used in the fiber optics world. EAMs are used as external modulators of light output from continuous wave lasers. For example, an EAM can be used with an inexpensive slow laser for a high-performance application, i.e. transmitting at data rates limited, not by the characteristics of the laser, but by the characteristics of the EAM.
In most applications of EAMs to date, the modulators and the electronics driving the modulator are separate chips mounted on a substrate and interconnected by a matched impedance strip-line circuit. At the speeds where EAMs are typically used, a matched impedance drive circuit is required, unless the interconnect length is much less than a wavelength. Commonly available packaging approaches do not meet this requirement and matched impedance interconnect is needed. However, use of a matched impedance strip-lines results in significant power loss, i.e. loss of half of the drive voltage due to the matched impedances. For a typical EAM drive voltage is in the order of 2 Volts, and an impedance of 50 Ohms, the drive power is quite high, because of the low impedance. To reduce power loss and improved performance, there is a need for alternative solutions that eliminate the need for matched impedance strip-lines.
Another issue is that EAMs are non-linear, temperature dependent and wavelength dependent. As such, they are normally used in applications where the modulation of the light is simple on-off modulation. Analog modulation schemes for high performance applications, such as optical data center interconnects, use other types of modulators, such as Mach-Zehnder (MZ) modulators. MZ modulators are typically larger, costlier and require a digital signal processor (DSP) or other methods to compensate for their sinusoidal modulation function.
There is a need for electro-absorption modulators with improved linearization and temperature compensation, particularly for applications such as high speed optical data center interconnects.